Mechanical and chemical-mechanical planarization (“CMP”) processes remove material from the surface of microfeature workpieces in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a carrier head 30, and a planarizing pad 40. The CMP machine 10 may also include an under-pad 50 between an upper surface 22 of the platen 20 and a lower surface of the planarizing pad 40. The under-pad 50 provides a thermal and mechanical interface between the planarizing pad 40 and the platen 20. A drive assembly 26 rotates the platen 20 (indicated by arrow F) and/or reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 50, the planarizing pad 40 moves with the platen 20 during planarization.
The carrier head 30 has a lower surface 32 to which a microfeature workpiece 12 may be attached, or the workpiece 12 may be attached to a resilient pad 34 or bladder system. The carrier head 30 may be a weighted, free-floating wafer carrier, or an actuator assembly 31 may be attached to the carrier head 30 to impart rotational motion to the microfeature workpiece 12 (indicated by arrow J) and/or reciprocate the workpiece 12 back and forth (indicated by arrow 1).
The planarizing pad 40 and a planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the microfeature workpiece 12. The planarizing solution 44 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the microfeature workpiece 12.
To planarize the microfeature workpiece 12 with the CMP machine 10, the carrier head 30 presses the workpiece 12 facedown against the planarizing pad 40. More specifically, the carrier head 30 generally presses the microfeature workpiece 12 against the planarizing solution 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier head 30 moves to rub the workpiece 12 against the planarizing surface 42. As the microfeature workpiece 12 rubs against the planarizing surface 42, the planarizing medium removes material from the face of the workpiece 12. The force generated by friction between the microfeature workpiece 12 and the planarizing medium will, at any given instant, be exerted across the surface of the workpiece 12 primarily in the direction of the relative movement between the workpiece 12 and the planarizing pad 40. The carrier head 30 can include a retaining ring 33 to counter this force and hold the microfeature workpiece 12 in position.
The CMP process must consistently and accurately produce a uniformly planar surface without defects on workpieces to enable precise fabrication of circuits and photo-patterns. A nonuniform surface can result, for example, when the removal rate of material is not uniform across the surface of the workpiece. Defects in the form of voids, tear outs, indents, scratches or chatter marks can be caused by the interface between the workpiece, the planarizing solution, and the planarizing pad. The planarizing solution can greatly affect the nonuniformity in removal rates and the number of defects on a workpiece. For example, hard abrasive particles and/or large abrasive particles are a significant source of defects because they are more likely to cause scratches or other types of surface asperities on the workpiece. On the other hand, small particles have a very low polishing rate that is unacceptable in many applications, and small particles can also cause dishing because they are more likely to contact the inner portions of deep depressions on the workpiece. The problems associated with planarizing solutions are exacerbated as the feature sizes shrink because even slight defects and/or dishing can ruin such small features.
Composite Abrasive Slurries (CAS) show promising results in reducing defects and dishing. FIG. 2 schematically illustrates an existing CAS 44 that has been developed for CMP processing. The slurry 44 includes a liquid solution 60 and composite abrasive particles 70. The composite abrasive particles 70 have cores 72 with exterior surfaces 73 and a plurality of abrasive particles 74. The abrasive particles 74 are held to the exterior surface 73 of a core 72 by interaction forces, such as chemical bonding and/or electrical attraction forces. The cores 72 can be soft cores made from polymeric materials or hard cores made from large abrasive particles. In a soft core application, the composite abrasive particles 70 are formed by (a) forming polymeric microspheres without abrasive particles and then curing the microspheres to make the cores 72, (b) mixing the cores 72 and the abrasive particles 74 in a liquid solution such that the zeta potentials between the cores 72 and the abrasive particles 74 cause the particles 74 to be attracted to the exterior surfaces 73 of the cores 72, and (c) optionally chemically reacting the particles and polymer to form a chemical bond. The known composite abrasive particles 70 accordingly have abrasive particles 74 only on the exterior surfaces 73 of the cores 72.
Although the CAS 44 shown in FIG. 2 produces some desirable results, it also raises several problems for CMP processing. First, the composite abrasive particles 70 require very small abrasive particles 74 that are not readily available. This results in high material costs and requires complex manufacturing techniques to handle such particles. Second, the small abrasive particles 74 can be detached from the cores 72 because the interaction forces may not be sufficient to withstand the forces exerted against the composite abrasive particles 70 during a planarizing cycle. This results in a relatively slow polishing rate and dishing because the CAS 44 begins to act like a conventional CMP slurry with very small particles as more abrasive particles 74 become detached from the cores 72. Third, the liquid solution 60 and any cleaning solutions are limited to maintaining the zeta potentials between the cores 72 and the particles 74 so that the liquid solution 60 does not cause the cores 72 to repel the particles 74. This limits the composition of the cores 72 and the particles 74, and it also restricts the constituents of the planarizing solution. Therefore, existing CASs also have several problems and limitations. Similar limitations exist with mixed abrasive slurries in which different types of abrasive particles are mixed in a common solution.